hey there,

to add
{(2x−1)3x+8}=2x−13x+18.
you multiply the denominator of first part with the numerator of second part and the denominator of the second part by the numerator of first part, and then divide the whole expression by the product of the denominators that is
{(2x−1)3x+18}=(2x−1)(1)3x(1)+8(2x−1).
hope it helped , and yes it is a polynomial , a polynomial is defined as ax
n + bx + c where n can be any whole numbers that are 0,1,2,3.....n, , the highest power of x is known as the degree of polynomial as in this case there are two powers of x that are :1 and n, assuming n>1 then the given polynomial is said to be of degree n .